ipv6: fib6_info_destroy_rcu() cleanup

We do not need to clear f6i->rt6i_exception_bucket right before
freeing f6i.

Note that f6i->rt6i_exception_bucket is properly protected by
f6i->exception_bucket_flushed being set to one in rt6_flush_exceptions()
under the protection of rt6_exception_lock.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Wei Wang <weiwan@google.com>
Acked-by: Wei Wang <weiwan@google.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>